In an electric power tool including a removably mounted battery pack as its power source, a lock unit for keeping the battery pack mounted to a tool body is provided so that the integrity of electric connection between the tool body and the battery pack should not be impaired by the vibration generated when performing a work with the electric power tool. In order to avoid generation of looseness between the tool body and the battery pack as far as possible, the lock unit is configured not to come into a connection-keeping state (namely, a locked state) unless the battery pack is completely mounted to the tool body (see, e.g., Japanese Patent Laid-open Publication No. 2001-143678).
The battery pack and the tool body are connected to each other through a current supplying terminal portion which is designed to have a specified over-travel amount for enhancement of its reliability.
For that reason, it is often the case that an electric current is supplied from the battery pack to the tool body even when the battery pack is not completely mounted to the tool body and the lock unit is not in the locked state. If a user unknowingly operates a switch of the tool body in this state, there may occur a situation that the electric power tool comes to be normally operated. In this case, the battery pack may possibly be dropped from the tool body if the user continues to use the electric power tool in that state.